Ethanol is manufactured by reacting ethene with steam. The catalyst used is silicon dioxide which is coated with a solid phosphoric acid.The reaction is reversible, and the formation of the ethanol is exothermic.

Only 5% of the ethene is converted into ethanol at each pass through the reactor. By removing the ethanol from the equilibrium mixture and recycling the ethene, it is possible to achieve an overall 95% conversion.

A flow scheme for the reaction looks like this:

Note: This is a bit of a simplification! When the gases from the reactor are cooled, then excess steam will condense as well as the ethanol. The ethanol will have to be separated from the water by fractional distillation.

Raw materials derived from starch or cellulose must first be hydrolyzed to become sugar / sucrose to be fermented. In industrial scale, sucrose may not be used as a raw material. Rarefaction glucose require a long time if only to be used in fermentation.

The first stage in the fermentation process is the decomposition of complex carbohydrates into simple carbohydrates. For example, if raw materials used digunakanan is starch in grains such as wheat or rice, then the raw material is heated with hot water to extract the starch and subsequently heated with malate. Malate was germinated rice which contain enzymes that can break down starch into simpler carbohydrates, which is referred to as maltose, C12H22O11.

Yeast then incorporated and the mixture allowed to warm (around 35 ° C) for several days (30-40 hours) until fermentation is complete in anaerobic conditions. Air is not allowed into the mixture to prevent oxidation of ethanol produced into ethanoic acid (vinegar).

The enzymes in yeast convert carbohydrates such as maltose or sucrose into simpler carbohydrates such as glucose and fructose, both C6H12O6, and then transform these simple carbohydrates into ethanol and carbon dioxide. Occurring CO2 gas is collected in tanks & recovered. Fermented liquid is called beer.

These changes can be expressed as equations of simple chemical reactions, although the biochemical aspects of these reactions are far more complicated.

Yeast is turned off by the ethanol concentration about of 15%, and this limits the purity of ethanol can be produced. Ethanol is separated from the mixture by fractional distillation to yield pure 96% ethanol.
In theory, 4% of the last remaining water could not be removed by fractional distillation.

Comparison of Ethanol Manufacturing by Hydration of Ethane Method and Fermentation Method